L12

FibonacciTest.java

import java.util.*;

public class FibonacciTest {
    public static void main(String[] args) {
        Scanner myScanner = new Scanner(System.in);
        boolean done = false;
        while (!done) {
            System.out.print("Enter an integer or Q to quit: ");
            String answer = myScanner.nextLine();
            if (answer.equalsIgnoreCase("q"))
                done = true;
            else {
                int myLong = Integer.parseInt(answer);
                long startTime = System.currentTimeMillis();
                long fibN = fibonacci(myLong);
                long endTime = System.currentTimeMillis();
                double elapsedTime = (endTime - startTime) / 1000.0;
                System.out.print("Fibonacci(" + myLong + ") = " + fibN);
                System.out.println(" took " + elapsedTime + " seconds");
            }
        }
        System.out.println("Goodbye!");
    }

    public static long fibonacci(long n) {
        if (n <= 2) {
            if (n == 0)
                return (0);
            else
                return (1);
        } else
            return (fibonacci(n - 1) + fibonacci(n - 2));
    }
}

ExponentTest.java

import java.util.Scanner;

public class ExponentTest {
    public static void main(String[] args) {
        Scanner myScanner = new Scanner(System.in);
        boolean done = false;
        while (!done) {
            System.out.print("Enter an integer a then n to compute a^n or Q to quit: ");
            String answer = myScanner.nextLine();
            if (answer.equalsIgnoreCase("q"))
                done = true;
            else {
                int a = Integer.parseInt(answer);
                System.out.print("Enter an integer n: ");
                answer = myScanner.nextLine();
                int n = Integer.parseInt(answer);
                long startTime = System.currentTimeMillis();
                long exp = exponent(a, n);
                long endTime = System.currentTimeMillis();
                double elapsedTime = (endTime - startTime) / 1000.0;
                System.out.print("exponent(" + a + ", " + n + ") = " + exp);
                System.out.println(" took " + elapsedTime + " seconds");
            }
        }
        System.out.println("Goodbye!");
    }

    public static int exponent(int a, int n) {
        if (n > 1) {
            return a * exponent(a, n - 1);
        } else {
            return a;
        }
    }
}

Reverse.java

import java.util.Scanner;

public class Reverse {
    public static void main(String[] args) {
        Scanner myScanner = new Scanner(System.in);
        boolean done = false;
        while (!done) {
            System.out.print("Enter a string to reverse or Q to quit: ");
            String answer = myScanner.nextLine();
            if (answer.equalsIgnoreCase("q"))
                done = true;
            else {
                long startTime = System.currentTimeMillis();
                String rev = reverse(answer);
                long endTime = System.currentTimeMillis();
                double elapsedTime = (endTime - startTime) / 1000.0;
                System.out.print("reverse(" + answer + ") = " + rev);
                System.out.println(" took " + elapsedTime + " seconds");
            }
        }
        System.out.println("Goodbye!");
    }

    public static String reverse(String s) {
        if (s.length() > 0)
            return s.charAt(s.length() - 1) + reverse(s.substring(0, s.length() - 1));
        else
            return "";
    }
}